The present invention relates to a gas-liquid contact apparatus, and more particularly to a gas-liquid by generating a large number of fine gas bubbles in the liquid.
Hitherto, the following methods have been known in enhancing the efficiency of contact between gas and liquid by increasing a contact area of gas and liquid:
(1) A shaft or propeller of a propeller stirrer is of a hollow structure with perforations being formed in its side wall. Gas is supplied to the hollow shaft and ejected through the perforations to produce fine air bubbles.
(2) Gas is ejected into liquid through pores of unglazed pottery or the like to form fine air bubbles.
(3) Gas is supplied to an interior of a turbine blade to be ejected into the gas-liquid mixture.
(4) Liquid under pressure is supplied to a venturi tube and mixed with gas by the actions of suction and movement of gas in the tube.
However, those methods have the following disadvantages. In the above method (1), the effeciency of producing fine air bubbles is low, power consumption is high in stirring the liquid, average diameter of the air bubbles is relatively large, and a rate of miniaturization of gas is low. In the method (2), resistance of gas passing througn the pores is high, so that high compression power is required, clogging of the pores occurs frequently when the liquid to be treated contains hard-to-disslove or easy-to-deposit material, and the efficiency of contacting gas with liquid becomes low. In the method (3), power dissipation is high when a large scale apparatus is used; large size air bubbles increase and fine air bubbles cannot be produced when the amount of gas increases. In the method (4), a ratio of the amount of suction gas required to the amount of supplied liquid is small and power dissipation is relatively high.
In order to minimize the power dissipation while attaining a high efficiency of generation of fine air bubbles, a method has been proposed wherein gas is ejected from under a rotor having a vertical hollow cylindrical body which rotates horizontally at the bottom level in a liquid contact vessel so that a gas film is formed on the surface of the cylindrical body to enhance generation of fine air bubbles (See Japanese Patent Publication No. 43-13121 (1968)).
However, although the proposed method reduces the power dissipation, it can make only a small amount of fine air bubbles, and this trend becomes remarkable as the amount of air increases.
Furthermore, the apparatus having a cylindrical rotor with vertical axis has a drawback that the liquid is not stirred sufficiently throughout the whole vessel. Also, the vertical hollow cylindrical rotor requires special mechanism and special care for balancing the rotor when rotating.